add csi-test to vendor

vendor/github.com/golang/mock/sample/README.md

@@ -0,0 +1,16 @@
+This directory contains an example of a package containing a non-trivial
+interface that can be mocked with GoMock. The interesting files are:
+
+ *  `user.go`: Source code for the sample package, containing interfaces to be
+    mocked. This file depends on the packages named imp[1-4] for various things.
+
+ *  `user_test.go`: A test for the sample package, in which mocks of the
+    interfaces from `user.go` are used. This demonstrates how to create mock
+    objects, set up expectations, and so on.
+
+ *  `mock_user/mock_user.go`: The generated mock code. See ../update_mocks.sh
+    for the command used to generate it.
+
+To run the test,
+
+    go test github.com/golang/mock/sample